1. Field of the Invention
The present invention relates to a method according to the preamble of the appended claim 1. The invention relates to a mobile station according to the preamble of the appended claim 12.
2. Brief Description of Related Developments
A mobile communication system makes a wireless data transmission possible between a mobile station (MS) and the fixed parts in the system when the user moves within the operating range of the system. A typical system is the public land mobile network PLMN, an example of which to be mentioned is the widely known circuit-switched GSM system (Global System for Mobile Telecommunications). The present system is particularly applicable for mobile communication systems under development. As an example of such a mobile communication system, the GPRS system (General Packet Radio Service) will be used in this description. It is obvious that the invention can also be applied in other mobile communication systems (UMTS, 3G).
The basic idea of the GPRS system is to use packet-switched resource allocation, wherein resources, e.g. a logical radio channel for radio communication, are allocated when there is a need to transmit and at receive data and information. Thus, the use of the network and resources available is optimized, to be used as efficiently as possible e.g. in comparison with GSM technology. The GPRS is part of the so-called GSM phase 2+, with the purpose of offering packet-switched data transmission for GSM compatible mobile stations within the GSM infrastructure. In the GPRS system, the allocation of channels is conducted in a flexible manner; for example, for each mobile station, 1 to 8 logical channels can be allocated on a physical channel. The same resources can be allocated to a larger number of active mobile stations, and both uplink data transmission (i.e. data transmission from the mobile station to the base station) and downlink data transmission (i.e. data transmission from the base station to the mobile station) can be allocated separately for the users. The channels are used primarily as control channels and traffic channels. The traffic channels are used for the transmission of data, and the control channels are used for signalling between the base station subsystem (BSS) and the mobile stations (MS). In the GPRS system, the mobile communication network is supplemented with serving GPRS support nodes (SGSN) to offer packet transmission services for the mobile stations via the base transceiver stations (BTS).
The GPRS system makes data transmission more efficient, because the same physical radio channel can be used by several different mobile subscribers. Communication takes place via the mobile station and the base station only when needed, and the physical radio channel is not reserved for communication between the base station and one mobile station only. In the system, a so-called virtual data transmission connection exists between the mobile station and the network. In the GPRS system based on a cellular system, resources include radio channels used for data transmission (PDCH, Packet Data Channels). Signalling used for general control takes place on a PCCCH control channel (Packet Common Control Channel) reserved for that purpose.
More precisely, the physical PDCH channels are divided into logical radio channels by means of a multiframe consisting of 52 TDMA (Time Division Multiple Access) frames that are transmitted repeatedly and divided further into 12 radio blocks (RLC/MAC Block) or time slots which are each divided into 4 frames, and 4 idle frames. In communication, these are used for data transmission and signalling. The blocks are divided further into at least the following parts: MAC header (Medium Access Control Header) which comprises in the downlink direction a USF field (Uplink State Flag) and in the uplink direction an SI field (Stall Indicator), and a RLC data block (Radio Data Block) comprising a TFI field (Temporary Flow Identifier) and a BSN field (Block Sequence Number), or a RLC/MAC control block. The RLC data block comprises also the information to be transmitted, i.e. RLC data. An example of the block structure is illustrated in more detail in FIG. 1.
The BSN field (Block Sequence Number) indicates the respective order of RLC data blocks belonging to each TBF flow, wherein the BSN can have a value from 1 to 127. The SI field (Stall Indicator) indicates if the RLC window of the mobile station is stalled or not. The mobile station sets the value of the SI field in all the uplink blocks accordingly.
As shown in FIG. 2, the terms RLC and, MAC refer to protocol layers of the communication protocol used in the mobile station MS. The communication protocol and the different layers constitute the protocol means of the mobile station for processing and generating data that is received or to be transmitted. The functions of the known RLC/MAC layer 201 (Radio Link Control/Medium Access Control) are needed between the LLC (Logical Link Control) layer 202 and the physical layer 203 of the mobile station MS. Above the LLC layer 202 there are known GPRS mobility management functions (GMM/SM) 205, SNDCP (Subnetwork Dependent Convergency Protocol) functions 204 and also short message service (SMS) functions. The layers are described in more detail in the GSM standard specifications.
The MAC block is used for allocating radio channels between mobile stations as well as to allocate the physical radio channel for the mobile station for receiving and transmitting according to the need. The RLC block is responsible for e.g. the allocation of resources upon request for packets to be transmitted to the mobile communication network and for retransmission over the radio channel. The SNDCP is used as an interface for the PDP (Packet Data Protocol). The SNDCP block compresses the NPDU (Network Protocol Data Unit) blocks received by it and segments them in one or several LLC frames which are further segmented into RLC data blocks. The GMM protocol supports the functions of the mobility management of the mobile station, including loggings in and out (GPRS attach, GPRS detach) and activations (PDP Context Activation, PDP Context Deactivation). The lowermost level, i.e. the so-called physical layer 203 is responsible for the physical modulation of radio waves and the transmission of information between the mobile station and the network. The uppermost layer 206 comprises an application utilizing said protocol stack.
The communication protocol corresponding to that described above and the different layers are also formed in the network, in which the different layers can also be distributed between the base station subsystem, the serving GPRS support node and the gateway GPRS support node.
The basic idea of multiple access in the GPRS network is that the mobile station can receive all the information transmitted by the serving base station. Of the received RLC blocks, the mobile station finds out the data addressed to it. According to the GPRS system, all the mobile stations waiting for data to be transmitted to them on a jointly allocated channel receive also all the blocks of the frame structure with the RLC blocks, interpret the received information and the temporary flow identifier TFI received therewith.
The USF field can be given 8 different values, and the downlink USF value defines the mobile station for which the next corresponding uplink block is allocated for data transmission.
A so-called temporary block flow TBF is a logical connection supporting data transmission on physical packet data channels between a sender (such as a mobile station MS) and a receiver (such as a base transceiver station BTS in the network), particularly between end points which are located on the RLC layers of their communication protocols. For the TBF, resources are allocated on one or several PDCH channels, and it comprises several RLC/MAC blocks conveying information. The TBF is maintained during the data transmission, until all the RLC/MAC blocks are transmitted or the receiver has reported all the transmitted blocks to be received. Each uplink or downlink TBF is allocated an individual temporary flow identity TFI. With a PUA (Packet Uplink Assignment) or PDA (Packet Downlink Assignment) message received by the mobile station from the network, the mobile station is allocated number N (1 to 8) of PDCH channels to be monitored by the mobile station, wherein the value N depends on the MS multislot class, the number of which can at present range from 1 to 29.
With reference to FIG. 2, each transmitter uses a so-called transmit window with a predetermined size. Similarly, each receiver uses a so-called receive window with a predetermined size. The windows mentioned in this description will be jointly called a transfer window. At the present, in the GPRS and EGPRS (Enhanced Packet Radio Service) systems the size k for both windows is defined as a standard window size k=64, i.e. 64 data blocks (RLC data blocks), within which the transmission takes place. Correctly received data blocks are acknowledged to the transmitter which “transfers” the window forward and makes it possible to transmit new data blocks. In addition to this, the receiver may transmit request for retransmission of incorrect data blocks, after whose acknowledgement the window is also “transferred”. In some situations, the window is “stalled”, wherein the transmission of new data blocks is interrupted. With an increase in the properties of mobile station so that the number of data blocks received in the same time unit is increased, also interruptions have been found to occur more and more frequently.